Ballad operas and singspiels were similar because

The answer is they were both sung in the language of the audience. Ballad opera in English Combined spoken dialogue with simple songs accompanied by basso continuo, characters were taken from contemporary life, and plots often featured political satire, words were in vernacular, music was simple and had catchy tunes, developed in England while to singspiel  Employed spoken dialogue and vocal style more like song than elaborate aria, developed in Germany. 

they were both sung in the language of the audience (apex)

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